1. Field of the Invention
The present invention relates to a method of manufacturing preforms, and to an apparatus for use in manufacturing preforms. More particularly, the present invention relates to an apparatus which includes a horizontally translatable shuttle member on which a foraminous mold is placed in a manufacturing process.
2. Description of the Prior Art
The formation of preforms from chopped fiber materials such as glass fibers, in the formation of fiber reinforced plastics, is a known art. However, existing apparatus for use in forming fiber directed preforms suffer from several drawbacks.
In the past, preforms were generally prepared by placing a screen, configured to the desired shape of a preform to be produced, on a rotary device having a fan behind it. The fan was used to draw air through the screen and to create a vacuum to draw material onto the screen. Usually, a mixture of glass fibers and bonding material to hold the fibers together was sprayed onto the screen and accumulated thereon through the action of the fan. After the preform is made it is placed in an oven to affix the glass fiber particles together in order to permanently retain the preform in the shape of the screen. The preform is then removed from the screen, trimmed, and is placed in a hollow mold. A resin is then injected into the mold and surrounds the fiber particles to create a finished article.
A review of some current developments in the preform manufacturing industry is given in the January 1989 issue of PPG Industries' Reinforcement Digest on pages 18-21.
A brief review of some patents in the field of fiber preforms and related arts follows.
Hampshire U.S. Pat. No. 2,929,436 discloses a method and apparatus for spraying a mixture of fibers and resin material onto a screen which has a vacuum applied behind it to draw the fiber onto the screen. In the apparatus of Hampshire, three separate conduits allow for transport of fibers, liquid resin bonding material, and compressed air to direct the flow of the fiber material from the gun. The area to which the vacuum must be applied in the apparatus of Hampshire is quite large, and the gun thereof must be manually held and sprayed by an operator. Moreover, the screen mold is mounted vertically on a wall panel and thus gravity may be a problem in the application of the fibers to the screen in this apparatus. The wire mold remains in a fixed position throughout the application of the fibers and resin thereto in the apparatus of Hampshire.
Roscher et al., U.S. Pat. No. 3,328,383 discloses a process for making glass fiber mats. In the method of Roscher, substantially brittle thermoplastic synthetic resin filaments are formed and mixed with glass fiber filaments, the fibers and filaments being chopped and dispersed together into a glass mat or preform. In the apparatus of Roscher, a conveyor screen moves the mat along and the mat is compressed by rollers as it moves along the conveyor screen.
Hall U.S. Pat. No. 3,908,591 discloses an adjustable apparatus for applying a flowable binder to sheet material such as a glass fiber mat. The disclosure of Hall is directed to the high volume production of relatively flat sheets of material to be bound such as glass fiber mat.
Palmer et al., U.S. Pat. No. 4,379,798 discloses a three-dimensional woven reinforcement containing both graphite fibers and glass fiber layers. The woven assembly of Palmer is impregnated with a resin such as epoxy to form a structural component such as I-beam or the like to be used as a lightweight component in construction or a similar use.
Layden U.S. Pat. No. 4,412,854 discloses a method of producing fiber reinforced articles in which sheets of fiber reinforcement are impregnated with a layer of thermoplastic binder, dried and cut into preformed shapes. These are stacked in a mold and warm molded to form an intermediate article, and the intermediate article is then hot pressed in a mold to form a final article.
Generally in forming fiber preforms from glass fiber roving in the prior art, the speed of manufacturing preforms was quite limited by the use of only a single screen mold. Varied thickness within a single preform is very hard to obtain with the prior art devices. Often, the screen on which the fibers are being sprayed is rotated in the prior art, which creates stratified layers of fibers which may separate after the article is completed.
Although the prior art includes various methods of making fiber mats and preforms, a need still exists in the industry for a preform manufacturing apparatus which is simple and relatively inexpensive to manufacture and to operate. Moreover, a need also exists for a preform manufacturing apparatus which can vary the thickness within a single preform according to particular needs.